Transparent electrical conductors are widely used in the flat-panel display industry to form electrodes that are used to electrically switch light-emitting or light-transmitting properties of a display pixel, for example in liquid crystal or organic light-emitting diode displays. Transparent conductive electrodes are also used in touch screens in conjunction with displays. In such applications, the transparency and conductivity of the transparent electrodes are important attributes. In general, it is desired that transparent conductors have a high transparency (for example, greater than 90% in the visible spectrum) and a low electrical resistivity (for example, less than 10 ohms/square).
Transparent conductive electrodes used in touch screens are typically formed on a substrate that is mounted on a viewing surface of a display and the transparent electrodes are typically controlled by integrated circuit controllers mounted on a substrate separate from the touch screen substrate. The transparent conductive electrodes are electrically connected to their integrated circuit controllers through a flexible connector cable electrically connected to the transparent conductive electrode substrate. In some designs, the touch screen integrated circuit controllers are mounted on the flexible cable itself. The flexible connector cable is then electrically connected to other parts of the display and touch screen system. Such a conventional design requires two or three substrates, each with associated manufacturing steps, and electrical interconnections.
Transparent conductive electrodes are conventionally made of transparent conductive metal oxides. Such conductive materials are well known in the display and touch-screen industries and have a number of disadvantages, including limited transparency and conductivity and a tendency to crack under mechanical or environmental stress. Typical prior-art conductive electrode materials include conductive metal oxides such as indium tin oxide (ITO) or very thin layers of metal, for example silver or aluminum or metal alloys including silver or aluminum. These materials are coated, for example, by sputtering or vapor deposition, and are patterned on display or touch-screen substrates, such as glass. For example, the use of transparent conductive oxides to form arrays of touch sensors on one side of a substrate is taught in U.S. Patent Application Publication No. 2011/0099805 entitled “Method of Fabricating Capacitive Touch-Screen Panel”.
Transparent conductive metal oxides are increasingly expensive and relatively costly to deposit and pattern. Moreover, the substrate materials are limited by the electrode material deposition process (e.g. sputtering) and the current-carrying capacity of such electrodes is limited, thereby limiting the amount of power that can be supplied to the pixel elements. Although thicker layers of metal oxides or metals increase conductivity, they also reduce the transparency of the electrodes.
Transparent electrodes including very fine patterns of conductive elements, such as metal wires or conductive traces are known. For example, U.S. Patent Application Publication No. 2011/0007011 teaches a capacitive touch screen with a mesh electrode, as do U.S. Patent Application Publication No. 2010/0026664, U.S. Patent Application Publication No. 2010/0328248, and U.S. Pat. No. 8,179,381, which are hereby incorporated in their entirety by reference. As disclosed in U.S. Pat. No. 8,179,381, fine conductor patterns are made by one of several processes, including laser-cured masking, inkjet printing, gravure printing, micro-replication, and micro-contact printing. In particular, micro-replication is used to form micro-conductors formed in micro-replicated channels. The transparent micro-wire electrodes include micro-wires between 0.5μ and 4μ wide and a transparency of between approximately 86% and 96%.
Conductive micro-wires can be formed in micro-channels embossed in a substrate, for example as taught in CN102063951, which is hereby incorporated by reference in its entirety. As discussed in CN102063951, a pattern of micro-channels is formed in a substrate using an embossing technique. Embossing methods are generally known in the prior art and typically include coating a curable liquid, such as a polymer, onto a rigid substrate. A pattern of micro-channels is imprinted (impressed or embossed) onto the polymer layer by a master having an inverted pattern of structures formed on its surface. The polymer is then cured. A conductive ink is coated over the substrate and into the micro-channels, the excess conductive ink between micro-channels is removed, for example by mechanical buffing, patterned chemical electrolysis, or patterned chemical corrosion. The conductive ink in the micro-channels is cured, for example by heating. In an alternative method described in CN102063951, a photosensitive layer, chemical plating, or sputtering is used to pattern conductors, for example, using patterned radiation exposure or physical masks. Unwanted material (e.g. photosensitive resist) is removed, followed by electro-deposition of metallic ions in a bath.
Conductive micro-wires are used to form a touch switch, for example, as illustrated in U.S. Patent Application Publication No. 2011/0102370. In this example, a capacitive touch switch includes a first substrate on which is formed a first mesh-like electrode and a second substrate on which is formed a second mesh-like electrode. The first and second substrates are integrally bonded via an adhesive layer in such a manner that the first and second mesh-like electrodes face each other. Such a design requires the use of two substrates that are aligned and bonded together.
Multi-level masks are used with photo-lithography to form thin-film devices, for example as disclosed in U.S. Pat. No. 7,202,179. An imprinted 3D template structure is provided over multiple thin films formed on a substrate. The multiple levels of the template structure are used as masks for etching the thin films. This approach requires the use of a mask and multiple photo-lithographic steps.
The use of integrated circuits with electrical circuitry is well known. Various methods for providing integrated circuits on a substrate and electrically connecting them are also known. Integrated circuits can have a variety of sizes and packages. In one technique, Matsumura et al., in U.S. Patent Application Publication No. 2006/0055864, describes crystalline silicon substrates used for driving LCD displays. The application describes a method for selectively transferring and affixing pixel-control devices made from first semiconductor substrates onto a second planar display substrate. Wiring interconnections within the pixel-control device and connections from busses and control electrodes to the pixel-control device are shown.
Printed circuit boards are well known for electrically interconnecting integrated circuits and often include multiple layers of conductors with vias for electrically connecting conductors in different layers. Circuit boards are often made by etching conductive layers deposited on laminated fiberglass substrates. However, such etching processes are expensive and the substrates are not transparent and therefore of limited use in applications for which transparency is important, for example display and touch-screen applications.
Flexible substrates are also known in the art and are used with other devices, such as displays. U.S. Pat. No. 6,501,528 discloses a stacked display device with a folded substrate. U.S. Pat. No. 7,792,558 describes a mobile communication device with bent connector wires and U.S. Pat. No. 8,017,884 illustrates an integrated touch panel and electronic device. U.S. Pat. No. 5,520,112 describes a folded substrate and a dual-sided printing process. Such substrates, structures, and methods demonstrate an on-going need in the industry for manufacturing methods incorporating devices and flexible substrates.